Window defroster assembly with light control

ABSTRACT

A window defrost assembly having a substrate, a polycarbonate film adjacent to the substrate, a heater grid located between the substrate and the polycarbonate film, and a light control layer located between the polycarbonate film and the heater grid. The heater grid includes first and second bus bars and a plurality of grid lines extending between and connecting to the first and second bus bars.

BACKGROUND

1. Field of the Invention

This invention relates to a conductive heater grid design that providesperformance characteristics making it amenable for use in defrostingplastic and glass panels, such as windows in vehicles.

2. Related Technology

Plastic materials, such as polycarbonate (PC) andpolymethylmethyacrylate (PMMA), are currently being used in themanufacturing of numerous automotive parts and components, such asB-pillars, headlamps, and sunroofs. Automotive rear window (backlight)systems represent an application for these plastic materials due totheir many identified advantages, particularly in the areas ofstyling/design, weight savings, and safety/security. More specifically,plastic materials offer the automotive manufacturer the ability toreduce the complexity of the rear window assembly through theintegration of functional components into the molded plastic system, aswell as the ability to distinguish their vehicles by increasing overalldesign and shape complexity. Being lighter in weight than conventionalglass backlight systems, their incorporation into the vehicle mayfacilitate both a lower center of gravity for the vehicle (and thereforebetter vehicle handling & safety) and improved fuel economy. Further,enhanced safety is realized, particularly in a roll-over accidentbecause of a greater probability of the occupant or passenger beingretained in a vehicle.

Although there are many advantages associated with implementing plasticwindows, these windows are not without technical hurdles that must beaddressed prior to wide-scale commercial utilization. Limitationsrelating to material properties include the stability of plastics duringprolonged exposure to elevated temperatures and the limited ability ofplastics to conduct heat. Regarding the latter, in order to be used as arear window or backlight on a vehicle, the plastic material must becompatible with the use of a defroster or defogging system. Forcommercial acceptance, a plastic backlight must meet the performancecriteria established for the defrosting or defogging of glassbacklights.

The difference in material properties between glass and plastics becomesquite apparent when considering heat conduction. The thermalconductivity of glass (T_(c)=22.39 cal/cm-sec-° C.) is approximately 4-5times greater than that exhibited by a typical plastic (e.g., T_(c) forpolycarbonate=4.78 cal/cm-sec-° C.). Thus a defroster or defogger(hereafter just “defroster”) designed to work effectively on a glasswindow may not necessarily be efficient at defrosting, defogging ordeicing (hereafter just “defrosting” or “defrost”) a plastic window. Thelower thermal conductivity of the plastic may limit the dissipation ofheat from the heater grid lines across the surface of the plasticwindow. Thus, at a similar power output, a heater grid on a glass windowmay defrost the entire viewing area, while the same heater grid on aplastic window may only defrost those portions of the viewing area thatare close to the grid lines.

A second difference between glass and plastics that must be overcome isrelated to the electrical conductivity exhibited by a printed heatergrid. The thermal stability of glass, as demonstrated by a relativelyhigh softening temperature (e.g., T_(soften)>>1000° C.), allows for thesintering of a metallic paste on the surface of the glass window toyield a substantially inorganic frit or metallic wire. Since thesoftening temperature of glass is significantly greater than the glasstransition temperature of a typical plastic resin (e.g., polycarbonateT_(g)=145° C.), a metallic paste cannot be sintered onto a plasticpanel. Rather, it must be cured on the panel at a temperature lower thanthe T_(g) of the plastic resin.

From the above, it is seen that there is a need in the industry for asystem that will effectively defrost a plastic window with performancecharacteristics similar to that of a conventional glass window.

SUMMARY

In overcoming the drawbacks and limitations of the known art, thepresent invention provides a window assembly having defrostingcapabilities. The window assembly includes a substrate, a plastic filmadjacent to one side of the substrate, a heater grid located between thesubstrate and the plastic film and a light control layer located betweenthe plastic film and the heater grid. The light control layer may be anelectrochromic layer or a photochromic layer, or a thermochromic layer,or solar control layer.

The heater grid or conductive elements includes two generally opposedbus bars having a plurality of lines extending between the bus bars.Upon the application of a voltage to the heater grid, a current willflow through the grid lines from one bus bar to the other. As a result,the grid lines will heat up via resistive heating.

Further objects, features and advantages of this invention will becomereadily apparent to persons skilled in the art after a review of thefollowing description, with reference to the drawings and claims thatare appended to and form a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an automobile having a window panelassembly embodying the principles of the present invention;

FIG. 2 is a diagrammatic representation of a heater grid incorporatedinto a window panel assembly embodying the principles of the presentinvention;

FIG. 3A is a diagrammatic sectional view of a portion of the windowassembly generally taken along lines 3-3 in FIG. 2;

FIG. 3B is a cross sectional view similar to FIG. 3A of the windowassembly and further having a coating layer on both sides of the windowassembly;

FIG. 3C is a diagrammatic sectional view similar to FIG. 3A of thewindow assembly and further having a light emissive layer;

FIG. 3D is a diagrammatic sectional view of similar to FIG. 3A of thewindow assembly and further having a light emissive layer and aweathering layer; and

FIG. 4 illustrates a method of making the window assembly embodying theprinciples of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, an automobile 10 incorporating the presentinvention is shown therein. The automobile 10 has an occupantcompartment 11 located within. The automobile 10 includes a windowdefroster assembly 12 mounted via a frame 14 to the automobile 10.

Although this description describes using the window defroster assembly12 as a rear window, the invention is equally applicable to other areasof the automobile 10. For example, the window defroster assembly 12 maybe appropriately located and dimensioned to be used as a driver sidewindow, a passenger side window, rear windows, a front windshield and/orany other windows the automobile 10 may have.

Referring to FIG. 2, a more detailed view of the window defrosterassembly 12 is shown. The window defroster assembly 12 includes a heatergrid 16 having a series of grid lines 18 extending between generallyopposed bus bars 20, 22. As further discussed below, the heater grid 16is embedded within the window defroster assembly 12.

The bus bars 20, 22 are respectively designated as positive and negativebus bars. The bus bars 20, 22 each are accordingly coupled in one ormore places to leads 24, 26. Lead 24 is coupled to a positive terminal30 of a voltage source 28, while lead 26 is coupled to a negative(ground) terminal 32 of the a voltage source 28, thereby establishing anelectric circuit. The voltage source 28 may be the electrical system ofthe automobile 10. Such an electrical system is typically a 12 voltsystem. Upon the application of voltage to the heater grid 16, a currentwill flow through the grid lines 18 from the positive bus bar 20 to thenegative bus bar 22 and, as a result, the grid lines 18 will heat up viaresistive heating.

Referring to FIG. 3A, a cross section of a portion of the windowdefroster assembly 12, generally taken along lines 3-3 in FIG. 2, isshown therein. The window defroster assembly 12 includes a substrate 34having a first side 36 and a bottom side 38. Generally, the second side38 of the substrate 34 faces towards the occupant compartment 11 of theautomobile 10 while the first side 36 of the substrate 34 faces awayfrom the occupant compartment 11 of the automobile 10. The substrate 34may be made of polycarbonate (PC), polymethylmethyacrylate (PMMA),polyester, thermoplastic polyurethane (TPU), PX/polyester blends, PC/ABSor PC/ASA blend with/without glass fibers, and any combination thereof.Preferably, the substrate 34 is transparent.

Located above the first side 36 of the substrate 34 is a light controlassembly 39. In this embodiment, the light control assembly 39 includesa light control layer 42, a first plastic film 40 and/or a secondplastic film plastic film 41. In one embodiment, the light controlassembly 42 is sandwiched between the first plastic film 40 and thesecond plastic film plastic film 42. Generally, the first and secondplastic films 40, 41 are made of at least PC, PMMA polyester, TPU, andcombinations thereof.

The light control layer 42 may be made of a photochromic, anelectrochromic or a thermochromic device, or a solar control device. Thephotochromic material is a material that changes from being transparentto less transparent or even opaque when the photochromic material isexposed to light and reverts to transparency when the light is dimmed orblocked. The electrochromic layer may be multi-layer system, is at leastone of liquid-crystal based, suspended particle device (SPD) based,inorganic, organic, or hybrid based materials.

The electrochromic device consists of a sandwich of materials. Oneembodiment of this sandwich but not limited to this, comprises twoelectrode layers sandwiching an ion storage layer, an ionconductor/electrolyte layer and an electrochromic material layer. Thephotochromic can be single or multi-layer, it is at least one of TPU,PC, PMMA, polyester or other transparent thermoplastic or thermosettingmaterial/component further comprising photochromic dyes or pigments oradditives. When a voltage is applied to the electrochromic device asmall electric charge consisting of ions flows from the ion storagelayer into the electrochromic material layer via the ionconductor/electrolyte layer thus causing a chemical reaction in theelectrochromic material layer which results in a change from transparentto less transparent or even opaque. When the voltage direction isreversed the ions flow back to the ion storage layer so that theelectrochromic device reverts to transparency.

The thermochromic device contains materials change reversibly color withchanges in temperature, or allow for a visual response to changes intemperature. When the temperature is raised to a specified temperaturethe pigment goes from colorless or light color to colored or dark color.The pigment returns to the original color as it cools down. Thethermochromic material can be made as semi-conductor compounds, fromliquid crystals or using metal compounds, or organic pigments which arecomposed of micro capsules.

The solar control device may utilize solar absorbing pigment/additive orsolar reflective coating/ink/pigment to control the amount of infraredlight into the occupant compartment of the vehicle. A solar controllayer suitable for incorporation in the present invention is describedin U.S. application Ser. No. 11/450,732, which is herein incorporated byreference and is commonly owned.

Located between the light control assembly 39 and the first side 36 ofthe substrate 34 is the heater grid 16. The heater grid 16 may includeall or a portion of the grid lines 18 and the bus bars 20, 22 as bestshown in FIG. 2. The heater grid 16 may be printed directly onto thefirst plastic film 40 and/or the light control layer 42. Printing may beaffected using a conductive ink or paste and any method known to thoseskilled in the art including, but not limited to, screen-printing, padprinting, ink jet, or automatic dispensing. Automatic dispensingincludes techniques known to those skilled in the art of adhesiveapplication, such as drip & drag, streaming, and simple flow dispensing.Additionally or alternatively, an antenna trace similar to the heatergrid 16, may be printed directly on the plastic film 40 and/or the lightcontrol layer 42.

The heater grid 16 may be formed from any conductive material includingconductive pastes, inks, paints, coatings, wires/thin wires, or filmsknown to those skilled in the art. If the conductive element is a paste,ink, or paint, it is preferred that they include conductive particles(and nano-particles), flakes, or powders dispersed in a polymericmatrix. This polymeric matrix is preferably an epoxy resin, a polyesterresin, a polyvinyl acetate resin, a polyvinylchloride resin, apolyurethane resin or mixtures, blends, and copolymers of the like.

The conductive particles, flakes or powders may be of a metal including,but not limited to, silver, copper, zinc, aluminum, magnesium, nickel,tin, or mixtures and alloys of the like, as well as any metalliccompound, such as a metallic dichalcongenide. These conductiveparticles, flakes, or powders may also be any conductive organicmaterial known to those skilled in the art, such as polyaniline,amorphous carbon, carbon-graphite and carbon nanotubes. Although theparticle size of any particles, flakes, or powders may vary, a diameterof less than about 40 μm is preferred with a diameter of less than about1 μm being specifically preferred. Any solvents, which act as thecarrier medium in the conductive pastes, inks, or paints, may be amixture of any organic that provides solubility for the organic resin.Examples of metallic pastes, inks, or paints include silver-filledcompositions commercially available from DuPont Electronic Materials,Research Triangle Park, N.C. (5000 Membrane Switch, 5029 ConductorComposition, 5021 Silver Conductor, and 5096 Silver Conductor), AchesonColloids, Port Huron, Mich. (PF-007 and Electrodag SP-405), MethodeEngineering, Chicago, Ill. (31-1A Silver Composition, 31-3A SilverComposition), Creative Materials Inc., Tyngsboro, Mass. (118-029 2kSilver), and Advanced Conductive Materials, Atascadero, Calif. (PTF-12).

An ink layer 44 may be disposed between the heater gird 16 and the firstplastic film 40 and/or the light control layer 42. The ink layer 44 maybe disposed such that to cover areas of the heater grid 16, such as thebus bars 20, 22 from view. Additionally, the ink layer 44 may bestylized in such a way to provide for manufacturers to differentiatetheir window defroster assembly 12 from competitors. As such, the inklayer 44 may be stylized in any one of a number of patterns.

Placed above the light control assembly 39 are an optional firstweathering layer 46 and a first plasma layer 48 respectively. The firstweathering layer 46 may be a material that includes the basic chemistryof acrylic, polyurethane, siloxane, or a combination of these materialsto provide high weatherablity and long term ultraviolet. Further, thefirst weathering layer 46 may also include a material having lonomer orflouropolymer chemistry or similar material. Moreover, in anotherembodiment of the present invention silicon/nanoparticles may be blendedinto the material of the first weathering layer 46 or a silioxyanecopolymer is formed into the weathering layer 46 by polymerization. Theweathering layer 46 may be applied by one method selected from the groupof flow coating, dip coating, spray coating, in-mold coating, curtaincoating, and the like. If it's a weathering film, the weathering layer46 is produced by extrusion, co-extrusion, lamination,extrusion-lamination, extrusion-coating, roller-coating, and the like.The weathering layer 46 may include ultraviolet absorbers.

The first plasma layer 48 is a “glass-like” coating deposited on theweathering layer 46 by plasma enhanced chemical vapor deposition (PECVD)process, expanding thermal plasma PECVD, plasma polymerization,photochemical vapor deposition, ion beam deposition, ion platingdeposition, cathodic arc deposition, sputtering, evaporation,hollow-cathode activated deposition, magnetron activated deposition,activated reactive evaporation, thermal chemical vapor deposition, and asol-gel coating process or the like. An optional second weathering layer46′ and a second plasma layer 48′ may be deposited on the second side 38of the substrate 34. The plasma layers 48, 48′ may be multiple layersand may contain an ultraviolet absorber.

The plasma layers 48, 48′ may be made of aluminum oxide, bariumfluoride, boron nitride, hafnium oxide, lanthanum fluoride, magnesiumoxide, scandium oxide, silicon monoxide, silicon dioxide, siliconnitride, silicon oxy-nitride, silicon oxy-carbide, hydrogenated siliconoxy-carbide, silicon carbide, tantalum oxide, titanium oxide, tin oxide,yttrium oxide, zinc oxide, zinc selenide, zinc sulphide, zirconiumoxide, and zirconium titanate. Furthermore, the plasma layers 58, 60 maycomprise multiple sub-layers differing in composition or structure.

Referring to FIG. 3B, an alternative embodiment of the window defrosterassembly 12 is shown. This embodiment is similar to the embodiment shownin FIG. 3A. The difference is that this the light control assembly 39does not include the first and second plastic film 40, 41.

Referring to FIG. 3C, another alternative construction for the windowdefroster assembly 12 is shown. While this embodiment is similar to theembodiment shown in FIG. 3A, it varies in that it includes a lightemissive layer 50 and a plastic film layer 51 located between the secondside 38 of the substrate 34 and the second plasma layer 48′. The lightemissive layer 50 may emit light through the plastic film layer 51 tothe second plasma layer 48′ and into the occupant compartment 11 of theautomobile 10 as best shown in FIG. 1. A light emissive layer 50suitable for incorporation in the present invention is described in U.S.application Ser. No. 11/317,587 which is herein incorporated byreference and is commonly owned.

Referring to FIG. 3D, another alternative construction for the windowdefroster assembly 12 is shown. While this embodiment is similar to theembodiment shown in FIG. 3B, it varies in that it includes a lightemissive layer 50 and a plastic film layer 51 located between the secondside 38 of the substrate 34 and the second plasma layer 48′. The lightemissive layer 50 may emit light through and the plastic film layer 51to the second plasma layer 48′ and into the occupant compartment 11 ofthe automobile 10 as best shown in FIG. 1.

Referring to FIG. 4, a method 60 of producing the window assembly 12 isshown. First, as indicated by block 62, the light control assembly isformed. The light control assembly may be formed by extrusion,co-extrusion, lamination, extrusion-lamination, printing, coating,solvent casting, sputtering, electrochemical deposition, or similarprocess.

As shown in block 64, an ink layer and heater grid may be applied to thelight control assembly. The stylized ink layer and the heater grid maybe applied by screen printing, pad printing, membrane image transferprinting, transfer printing, ink jet printing, digital printing, roboticdispensing, or mask and spray. Optionally, as indicated by block 66, thelight control assembly may be thermoformed. This thermoforming processmay be done by vacuum thermoforming, pressure assisted thermoforming,drape forming or cold forming.

Thereafter, as shown in blocks 68 and 70, the light control assembly isthen trimmed and positioned to fit in a mold cavity. Once in the moldcavity, as shown in block 72, the light control assembly is back moldedwith a substrate material. This may be accomplished by utilizinginjection molding, compression molding, injection-compression molding,multi-component molding, multi-color molding or multi-material moldingprocess. The same method may apply when incorporating a light emissivelayer.

Afterwards, as indicated by blocks 74 and 76, the light control assemblyand substrate material are hot melted, thereby forming the window panel,which is then removed from the mold cavity. As shown in block 78, anoptional weathering layer may be applied to the window assembly.Thereafter, a plasma coating is applied to the window assembly via aPECVD process as shown in block 80.

The method 60 may also be executed when incorporating a light emissivelayer. This act would include the steps of the forming a light emissiveassembly, trimming the light emissive assembly, position the lightemissive assembly in the mold cavity, back molding the light emissiveassembly to the plastic substrate material, melt bonding the lightemissive assembly to form the window assembly, removing the windowassembly from the mold cavity, and applying a plasma coating on at leastone side of the window assembly.

As a person skilled in the art will readily appreciate, the abovedescription is meant as an illustration of implementation of theprinciples of this invention. This description is not intended to limitthe scope or application of this invention in that the invention issusceptible to modification, variation and change, without departingfrom spirit of this invention, as defined in the following claims.

1. A window defroster assembly having defrosting properties, the windowassembly comprising: a transparent substrate having a first side and asecond side; a light control assembly overlying the first side of thesubstrate; and a heater grid having first and second bus bars and aplurality of grid lines extending between and connected to the first andsecond bus bars, the heater grid located between the first side of thesubstrate and the light control assembly.
 2. The assembly of claim 1,wherein the substrate is made from a material selected from the groupincluding at least one of polycarbonate, polymethyl methacrylate,polyester, polyurethane, thermoplastic polyurethane, polyamide, blendsor copolymers, and combinations thereof.
 3. The assembly of claim 1,wherein the light control assembly comprises a first plastic film, asecond plastic film and a light control layer, the light control layerbeing located between the first and second plastic films.
 4. Theassembly of claim 1, wherein at least on of the first and second plasticfilms are made from a material selected from the group including atleast one of polycarbonate, polymethyl methyacrylate, polyester,polyurethane, thermoplastic polyurethane, polyamide, blends orcopolymers, and combinations thereof.
 5. The assembly of claim 1,further comprising a weathering layer applied over or within the lightcontrol assembly.
 6. The assembly of claim 5, wherein the weatheringlayer is made from at least one of acrylic, polyurethane, siloxane,silicone coating, lonomer, flouropolymer, ultraviolet absorbers,ultraviolet stabilizers, and combinations thereof.
 7. The assembly ofclaim 5, further comprising a plasma layer applied over the weatheringlayer.
 8. The assembly of claim 1, further comprising a plasma layeroverlying the second side of the substrate.
 9. The assembly of claim 8,further comprising a weathering layer located between the second side ofthe substrate and the plasma layer.
 10. The assembly of claim 9, whereinthe weathering layer is made from at least one material selected fromthe group of acrylic, polyurethane, siloxane, silicone coating, lonomer,flouropolymer, ultraviolet absorbers, ultraviolet stabilizers, andcombinations thereof.
 11. The assembly of claim 1, further comprising alight emissive layer located between the second side of the substrateand the plasma layer.
 12. The assembly of claim 1, wherein the heatergrid is made of conductive material.
 13. The assembly of claim 12,wherein the conductive material is at least one of silver, copper, zinc,aluminum, magnesium, nickel, tin and combinations thereof.
 14. Theassembly of claim 1, wherein the heater grid is at least one of aconductive paste, a conductive ink and a conductive paint/coating, aconductive wire and combinations thereof.
 15. The assembly of claim 1,wherein the light control assembly is an electrochromic layer.
 16. Theassembly of claim 15, wherein the electrochromic layer is at least oneof liquid-crystal based, suspended particle device (SPD) based,inorganic, organic, or hybrid based materials.
 17. The assembly of claim1, wherein the light control assembly is a photochromic layer.
 18. Theassembly of claim 17, wherein the photochromic layer is at least one ofTPU, PC, PMMA, polyester or other transparent thermoplastic orthermosetting material/component further comprising photochromic dyes orpigments or additives.
 19. The assembly of claim 1, wherein the lightcontrol assembly is a thermochromic layer.
 20. The assembly of claim 19,wherein the thermochromic material layer is at least one ofsemi-conductor compounds, metal compounds and organic pigments.
 21. Theassembly of claim 1, wherein the light control assembly is a solarcontrol layer, which may comprise of IR absorbers/layers or IRreflective coating/ink/pigments.
 22. The assembly of claim 1, furthercomprising an ink layer located between the heater grind and the lightcontrol assembly.
 23. A method of producing a window assembly, themethod comprising the steps of: forming a light control assembly;trimming the light control assembly; positioning the light controlassembly in a mold cavity; back molding the mold cavity with a plasticsubstrate material; melt bonding the light control assembly to theplastic substrate material to form the window assembly; removing thewindow assembly from the mold cavity; and applying a plasma coating onat least one side of the window assembly.
 24. The method of claim 23,further comprising the step of printing a stylized ink on the lightcontrol assembly.
 25. The method of claim 23, further comprising thestep of thermoforming the light control assembly.
 26. The method ofclaim 23, further comprising the step applying a weathering layer to thewindow assembly.
 27. The method of claim 23, wherein the light controlassembly further comprising a heater grid.
 28. The method of claim 23,further comprising the steps of: forming a light emissive assembly;trimming the light emissive assembly; position the light emissiveassembly in the mold cavity; back molding the light emissive assembly tothe plastic substrate material; melt bonding the light emissive assemblyto form the window assembly; removing the window assembly from the moldcavity; and applying a plasma coating on at least one side of the windowassembly.